This invention relates to control of rear wheel steering in a four-wheel steer vehicle, and in particular to a method for automatically disabling rear wheel steering upon certain limited conditions.
In four-wheel steering capable vehicles, an electronically controlled rear wheel steering system typically permits the rear wheels to be steered a proportional amount of front wheel steering in response to front wheel steering inputs. Normally rear wheel steering is strictly a user-selectable function permitting switching between four-wheel steering and front-wheel steering-only modes. One notable difference between four-wheel steer trucks and four-wheel steer cars is the use of a wider track width for rear wheels in some of the larger pickup trucks. Thus in a given truck, the rear track can be considerably wider than the front track width. Track width is herein defined as the measured distance between the outside of the left tire to the outside of the right tire on a given axle.
The use of larger track widths has given rise to the exacerbation of a problem with four-wheel steerable vehicles when used in automatic car wash assemblies. When the four-wheel steering mode is active and front steering inputs are induced via car wash rails, the rear wheels are indirectly steered for proper tracking between the car wash rails. When this occurs, particularly in the case of larger rear track widths, it has been noted that the rear tires of the vehicle have greater tendency to scrub, or even to occasionally become bound, against the rails of the car wash mechanism, temporarily disrupting car wash operations.
Unfortunately, it is not always feasible to rely upon the vehicle user to remember to deactivate the four-wheel steering mode to avoid the issue.
This invention provides an algorithm control solution to avoid the binding of four-wheel steerable vehicle wheels against the rails of a car wash mechanism, irrespective of active steering mode. Upon selection of a neutral gear, with four-wheel steering enabled, and at low vehicle speeds, the four-wheel steerable system will automatically switch into a two-wheel steering, or front steering only, mode. An algorithm control unit will disable the rear-wheel steering function, returning the rear wheels to their centered, non-angled, positions to eliminate binding of the rear wheels against the car wash rails as the vehicle is being pulled forward in a car wash assembly.
Since rear steering capability of a four-wheel steer vehicle is generally user-selectable between the modes of two-wheel steering and four-wheel steering, the algorithm control unit of the present invention provides that in the event that the vehicle enters a car wash in the four-wheel steering mode, the four-wheel mode will be automatically switched to the two-wheel mode, thus avoiding potential binding of the rear wheels. The invention also contemplates a solution to an increased likelihood of a wide rear track vehicle having its rear wheels bind between car wash rails, during the condition that the rear wheels of such vehicle are being steered; i.e. in a four-wheel steer mode.
In one preferred embodiment of the present invention, the vehicle will automatically enter into the two-wheel steering mode whenever the neutral gear of the transmission is selected, and the vehicle speed is less than five miles per hour, conditions likely to be encountered while a vehicle is being pulled through an automatic car wash assembly. dr
FIG. 1 is an elevation view of a four-wheel steerable truck vehicle of the type that includes a set of rear wheels having a wider track than the track of the front wheels of same vehicle.
FIG. 2 is a schematic diagram of the four-wheel steerable system showing the master algorithm control unit for determining relative rear wheel positions.
FIG. 3 is a schematic diagram of the system of FIG. 2, shown representing a vehicle positioned between parallel rails of a car wash assembly.
FIG. 4 displays an algorithm control sequence for disabling rear wheel steering in a four-wheel steer vehicle.